BRACHIOPODA. 



581 



cavity, and extend into the lacunae of the mantle where they may 

 be considerably ramified. The ripe sexual cells are dehisced into 

 the coelom, whence they pass to the exterior through the nephridia. 

 In some genera (Tliecidium, Cistella, Argiope) the eggs undergo the 



St' 



FIG. 464. Development of Argiope (after Kowalewsky). a, embryo in which the enteron D 

 still communicates in front with the coelomic sacs Lh. b, embryo with three segments, and 

 commencing mantle fold with setae, c, older embryo showing the same features ; M mantle 

 fold, d, free larva with eye spots, cephalic umbrella, ciliated ring, and large mantle lobes, 

 e, attached larva with mantle lobes bent anteriorly. /, later stage with tentacles T, and 

 commencing peduncle St. 



first stages of their development in brood-pouches placed near the 

 openings of the nephridia. In Thecidium the brood-pouch is median 

 and ventral. In Argiope and Cistella it is paired. 



Our knowledge of the development is very incomplete, and what 

 we do know relates almost entirely to the Testicardines. The egg 



